Preparation of high v.i. lube oils

ABSTRACT

EXTRACTION WITH A SOLVENT HAVING PREFERENTIAL SOLUBILITY FOR AROMATICS, AND INCLUDING THE IMPROVEMENT HEREIN COMPRISING SEPARATIONG THE SOLVENT AND EXTRACT FROM THE LUBRICATING OIL RAFFINATE PRODUCT OF SAID SECOND EXTRACTION AND EMPLOYING SAID SOLVENT WITH PRODUCT EXTRACT THEREIN FOR THE EXTRACTION OF HYDROCRACKER CHARGE STOCK IN SAID FIRST EXTRACTION.   A PROCESS FOR PRODUCING HIGH QUALITY AND HIGHLY STABLE LUBRICATING OILS WITH A HIGH VISOCITY INDEX WHEREIN A LUBRICATING OIL FRACTION IS FIRST SOLVENT EXTRACTED WITH A SOLVENT HAVING PREFERENTIAL SOLUBILITY FOR AROMATICS TO REDUCE THE POLYCYCLIC AROMATIC CONTENT THEREOF AND WHEREIN RAFFINATE FROM SAID EXTRACTION IS HYDROCRACKED UNDER CONDITIONS TO INCREASE THE VISCOSITY INDEX THEREOF AND WHEREIN HYDROCRACKED LUBRICATION OIL PRODUCT IS SUBJECTED TO A SECOND

May 18, 1971 w. w. WENTZHEIMER ETAL 3,579,431

PREPARATION OF HIGH V.I. LUBE OILS Filed April 5, 1969 RESIDUUM CRACKER RAFF'NATE FEED FEED SEPARATOR MAKE-UP 3 SOLVENT EXTRACTION soLvENTa. HYDRO- EXTRACT\ CRACKER 5 SOLVENT 7 9 LUBE SOLVENT SOLVENT PRODUCT 8 PRODUCT PRODUCT '5 RECOVERY EXTRACTION SEPARATOR EXTRACT RAFFINATE SOLVENT a EXTRACT INVENTORS= WILLIAM W. WENTZHEIMER RONALD W. REYNOLDS WILLIAM CHA (ATTORNEY United States Patent US. Cl. 208-87 6 Claims ABSTRACT OF THE DISCLOSURE A process for producing high quality and highly stable lubricating oils with a high viscosity index wherein a lubricating oil fraction is first solvent extracted with a solvent having preferential solubility for aromatics to reduce the polycyclic aromatic content thereof and wherein raffinate from said extraction is hydrocracked under conditions to increase the viscosity index thereof and wherein hydrocracked lubricating oil product is subjected to a second extraction with a solvent having preferential solubility for aromatics, and including the improvement herein comprising separating the solvent and extract from the lubricating oil rafifinate product of said second extraction and employing said solvent with product extract therein for the extraction of hydrocracker charge stock in said first extraction.

This invention broadly relates to the production of high V.I. lube oils and, more particularly, to improvements in a process scheme for producing high V.I. lube oils which are stable and of high quality.

RELATED APPLICATIONS The present invention is related to those described in U.S. applications Ser. No. 530,580, filed on Feb. 28, 1966, by Sheldon L. Thompson, and Ser. No. 743,915, filed July 3, 1968, by Rene F. Kress.

BACKGROUND OF THE INVENTION Various processes have been used from time to time for upgrading lubricating oil stocks and other petroleum fractions to lubricating oil stocks. These have generally involved either solvent extraction or hydrogenation including hydrocracking. Briefly, hydrocracking has involved treating the charge material over a catalyst at a temperature on the order of about 650 F. and above at high partial pressures of hydrogen. In more recent times, there has been an increased demand for lubricating oils having a high viscosity index. Recent developments, particularly in hydrocracking techniques, or hydrotreating techniques as some prefer to call it, has given birth to an increased interest in commercial utilization of such hydrogenation processes as a lubricating oil stock upgrading method in order to obtain lubricating oils with an increased viscosity index. This has been so in part at least because of the decline in availability of natural sources from which high V.I. lubes can be obtained by conventional techniques such as solvent extraction. The difiiculty of supplying this market is aggravated by the frequent demand for high V.I. lubes with still higher V.I. numbers.

In US. application Ser. No. 743,915, valuable improvements in the hydrocracking technique are described. In brief, the improvements involve solvent extracting at least part of the lube oil fraction to be hydrocracked with a solvent having preferential solubility for aromatics so as to selectively remove the more aromatic compounds (i.e., polycyclics containing multiple rings) which are more re- 3,579,437 Patented May 18, 1971 fractory under hydrocracking conditions and have a poor V.I. The highly aromatic extract is a good rubber oil stock, and the rafi inate can be hydrocracked at milder conditions to avoid overcracking of some of the lube oil material and to achive substantial economies in such a hydrocracking operation.

In US. application Ser. No. 530,580, a process is described by which the stability of hydrocracked product can be improved as to quality degradation on exposure to actinic light and oxygen. In brief, that process involves a relatively cool (as compared to conventional solvent refining), highly selective series of solvent extractions 0n the hydrocracked lube product. That extraction is so selective that even after about seven successive extractions the yields of rafiinate frequently exceed about and more usually are at least about 97%. Despite the small amount of aromatic material extracted, the solvent must be recovered relatively free of the aromatic in order to be reused effectively in stabilizing more hydrocracked product. Also, despite the fact that the amount of aromatic material extracted is small, it cannot be readily separated except by the conventional technique of distillation because it is soluble in the solvent. The entire amount of the solvent and oil extract solution must be distilled or otherwise fractionated to recover the solvent relatively free of the oil. At the same time, the solvent employed in the comparatively deep but selective extraction carried out on that lube oil fraction before it is hydrocracked as set forth in Ser. No. 743,915 must also be recovered in order to be reused in other extractions.

In a commercial operation it is necessary to recover and reuse the solvent from the extractions because the only alternative is to discharge the used solvent, which constitutes a greater economic loss than the cost of recovery of the solvent. An alternative to the foregoing choices (i.e., discharging the solvent after each use or purifying and recovering same) which would eliminate one or more operational steps and achive significant economies in a highly competitive market is desirous and accordingly to be commended.

SUMMARY OF THE INVENTION We have now found that the solvent and oil extract from the extraction of a lube oil fraction which has been hydrocracked over a lube oil hydrocracking catalyst at conditions whereby a lube oil fraction with an increased viscosity index (V.I.) is obtained, and which extraction is carried out with a solvent having preferential solubility for aromatics at a temperature and solvent dosage selected to provide for a high degree of selectivity for unstable polycyclic aromatic structures whereby said hydrocracked lube products have increased stability, can be reused without any purification or separation to solvent extract the virgin gas oil deasphalted residuum feed charged to the hydrocracker to reduce the polycyclic aromatic content of said feed to the hydrocracker.

THE DRAWING The figure is a digrammatical representation of an illustrative overall flow scheme of the present invention. A more detailed description will be found hereinbelow.

DETAILED DISCUSSION Each of the solvent extractions involved can be carried out in a fashion substantially identical to that wherein an entirely fresh solvent is employed for each of the extractions; i.e., the extraction of the hydrocracker feed charge and the post-hydrocracking stabilizing extraction. The hydrocracking step can likewise be carried out by any one of several known suitable techniques. We prefer to carry out the hydrocracking and prehydrocracking solvent extraction in substantially the same fashion as described in commonly assigned and copending application Ser. No. 743,915 referred to above. The important features of that step will be discussed briefly. Reference can be made to that application for any further information desired on that step.

Illustrative but nonlimiting examples of the solvents that can be employed in both extractions of the present invention are furfural, acetophenone, phenol, acetonitrile, nitrobenzene, aniline, 2,2-dichlorodiethyl ether, and dimethyl sulfoxide and mixtures thereof. The particular solvent selected is often dependent upon several considerations, not the least of which is economics; but, generally speaking, furfural and phenol are the more preferred solvents. With the exxception of those lubes or fractions which are of sufficiently low asphalt and metals content, the hydrocracker feed material is to be deasphalted before the first extraction. In the case of the relatively low asphalt stocks, the well-known Duo-Sol extraction procedure wherein deasphalting and aromatics extraction are carried out simultaneously is quite satisfactory. Known techniques for increasing selectivity for aromatics can be advantageously employed on occasion here. Examples of these are (1) providing for the presence of a small amount of water during the extraction with furfural, (2) operating in the lower portion of the suitable temperature range for the particular solvent, and (3) carrying out several extractions with a low ratio of solvent to oil and combinations of the foregoing.

The temperature of the extractions and solvent dosage is interdependent, and both the extraction and solvent dosage are in turn dependent upon the composition of the particular fraction being extracted. Accordingly, the following comments are to be understood as so qualified.

The temperature of all the prehydrocracking extractions must be below the temperature of miscibility of the oil and the solvent in order to have any extractive separation, and usually well below the temperature of miscibility for a highly efficient operation with good yields of oil as hydrocracker charge. The lower limit of temperature is controlled in part by the pour point of the charge when it has been dewaxed. If the charge has not been dewaxed, then the minimum temperature of the extraction is controlled by the point at which solids appear. However, in addition, if the extraction temperature is too low, the extraction will be too selective and require application of compensating features such as additional amounts of solvent and extraction stages; otherwise, the benefits accruing may be too limited. The temperature range encompassing all of the suitable operating temperatures for all of the solvents is, generally speaking, about to 350 F. In the case of furfural, however, a temperature in the more restricted range of about 125 to 325 F. is preferably employed. In the case of phenol, a temperature in the range of about 150 to 255 F. is usually preferred.

Most of the same comments above in regard to temperature are equally applicable to the ratio of solvent to oil employed. That is, the temperature and solvent ratios are interdependent upon each other, and each is in turn dependent upon the charge stock and principally its boiling range or molecular weight range. High ratios of solvent to oil, like high temperatures, tend to reduce the efiiciencies of the operation, producing lower yields of rafiinate as a hydrocracker charge, and are to be avoided. For the most part, at the suitable temperatures, solvent to oil ratios in the range of about 6:1 to about 0.25 :1 will be found suitable. However, ratios of solvent to oil on the order of about 4 to 08:1 will be found most preferred. It is believed that any further discussion of these variables will be better understood by reference to an example. Thus, a Lagomedio crude fraction boiling in the range of about 850 to 950 F. is preferably solvent extracted at a temperature of about 200 to 250 F. and a solvent dosage in the range of about 1:2 parts by volume of furfural per volume of treated oil. The fraction boiling above 950 F. from the same crude which has been deasphalted with propane is preferably solvent extracted at a temperature of about 225 to 275 F. and a solvent dosage of about 2:3 volumes of furfural per volume of treated oil. The fractions boiling below about 850 F. are generally not extracted because the benefits thereof are small relative to the cost. Fractions from other crudes, of course, would require some modification of the foregoing.

The equipment that may be employed is not critical as any conventional solvent extraction equipment can be employed. For example, rotating disc contactors, Podbielniak contactors, and countercurrent packed bed extraction columns may be named as illustrative. As will be apparent from the foregoing, the extraction can be carried out in either a batch-Wise operation or a continuouswise one, although the latter is generally found more convenient, economic, and preferred.

THE HYDROCRACKIN G OPERATION The residuum and distillates which have been extracted are then charged to a conventional lube oil hydrocracker (alone or blended with other suitable streams) and hydrocracked using conventional hydrocracking procedures. Illustrative but non-limiting examples of the hydrocracking procedure and modifications are US. Pat. Nos. 2,779,- 711, 2,917,448, 2,960,458, 3,046,218, 3,078,238, and 3,078,221. It is to be fully appreciated however that in the foregoing patents several clearly teach away from the present invention, indicating that the hydrocracker charge stock is not to be extracted with a solvent having preferential solubility for aromatics. As pointed out in Ser. No. 743,915 and in contradistinction to those teachings, an improved result can be obtained by such an extraction if employed in combination with milder hydrocracking conditions than are conventionally used. It has thus been discovered that those teachings are in error to the extent that they purport to apply to the procedure of the present invention as a whole. It is also desired to point out that such teachings are in error as to the requisite minimum viscosity of suitable charge stocks. In the present invention, charge stocks as low as about 45 to SUS at 210 F. can be employed. It is desired to make clear that the ranges taught by the art will work but are unduly limited for the present process. As the prior art indicates, the hydrocracker charge should generally have a V1. of at least about 60, and preferably at least about 75.

In brief, the preferred hydrocracking procedure comprises hydrocracking the solvent extracted material at about 650 to 825 F., but preferably between 700 and 800 F., at a pressure above about 1,500 p.s.i., but more usually and preferably above about 2,000 p.s.i., and at a liquid hourly space velocity between about 0.2 and 4.0, but more usually between about 0.4 and 1.5. The hydrocracking treatment is, of course, carried out in the presence of hydrogen over a hydrocrackin-g catalyst, i.e., a catalyst having both aromatic saturation and ringscission activity. Preferably, a sulfactive catalyst is employed. Sulfactive catalysts broadly comprse a sulfide of any metal of Group VI, left-hand column, of the periodic system of a sulfide of an iron group metal but preferably a sulfide of the Group VI metals mixed with a sulfide of an iron group metal; for example, a nickel sulfide and tungsten sulfide catalyst in about a 1:1 to 4:1 metal ratio respectively is excellent on an alumina, silica, or-aluminasilica base. Hydrocracking catalysts of free metals such as palladium on a mole-sieve base, etc., can be used but are less preferred.

POST-HYDROCRACKIN G EXTRACTION Solvent extraction following hydrocracking is disclosed in commonly assigned copending application Ser. No. 530,580. It was found in that invention that to accomplish the desired results of reduced quality degradation as to both sludge and color, not only is the temperature of the extraction important but also the number of stages is critical. The number of stages, however, is somewhat dependent upon the amount of solvent. It should be kept in mind in any discussion of these two variables that they vary in inverse fashion with respect to each other. When one is increased, the other is to be decreased. It has been discovered that the sludge formation is substantially eliminated in some instances with only two stages but that the color quality at the desirable level is not achieved unless at least about five stages are employed or unless excessive quantities of solvent are em ployed. Generally, from 3 to 10 stages will be found entirely suitable and preferred, and from 5 to stages are most preferred although more than 10 stages can be employed if desired.

The ratio of solvent to oil that can be employed in the extraction is not particularly critical, and ratios varying over a wide range can be employed; however, advantages obtain in using certain ratios. Generally, a ratio in excess of 2:1 of a solvent to oil is not employed because such increases the economic cost of the process due to the large volume of the solvent to be handled and reduces the yield of lubricating oil product. On the other hand, ratios lower than about 0.25:1 require a compensating increase in the number of stages to achieve the desired effect. Ratios of solvent to oil on the order of 0.5 to 1.25:1 are preferably employed.

The temperature will, of course, vary with the particular solvent employed in a given case. Generally, however, a temperature within the range of above about 0 to 300 F., is employed with any of those solvents taught herein. Of course, in order to obtain high selectivity, a narrower temperature within that range is to be employed with each of the suitable solvents. In the case of furfural, which is the most preferred solvent, a temperature in the range of above about 0 to about 150 F. can be advantageously employed; however, a temperature on the order of about 80 to 130 F. is preferred. The next preferred solvent is phenol or Selecto (phenol and a mixture of cresols), and the preferred temperature is above the melting point of phenol, i.e., about 106 to about 140 F, although the preferred temperature will vary on occasion.

Other examples of solvents that can be employed in this process are, of course, the same solvents or mixtures that are suitable for extracting the hydrocracker feed since using the same solvent in both extractions without an interim purification is an important feature of this invention.

The apparatus which can be employed to conduct the process is not special, and any of the conventional solvent extraction equipment may be employed for same. Illustrative but nonlimiting examples are rotating disc contactors, Podbielniak contactors, and countercurrent extraction columns, and the like. It is thus apparent that the same type of equipment is suitable in both of the extractions of this invention. Of the apparatus aforementioned, rotary disc contactors or columns are preferably employed in carrying out the invention. It will be appreciated that the extraction can be carried out in either a batch-wise or continuous-wise operation, although the latter is more convenient and is generally preferred. The equipment need not be adapted for special pressure conditions because atmospheric pressure is usually preferred.

In using the solvent-extract mixture from the product purification stage in the feed preparation extraction, some additional fresh furfural or other solvent will generally be added because large amounts of solvent are required there and also to compensate in some cases for the reduced extraction capacity due to the extract contained therein. The combined extracts from the two extraction operations can be cracked to gasoline. Alternatively, the combined extracts can be used as a rubber oil, but because of the presence of UV unstable compounds, a stabilizing treatment may be desirable in some cases.

6 ILLUSTRATIVE EXAMPLES Crude properties Gravity, API 32.9 Sulfur, wt. percent 01.26 SUS/l00 F. 52.7 Pour point, F. 30.0 CD. color 22270 The foregoing charge is vacuum distilled and the heaviest fraction (comprising about 23% of the crude) is propane deasphalted (yield of oil about 50%) to produce the following fractions:

Boiling range Light vacuum distillate About 775 to 855 F. Heavy vacuum distillate About 855 to 955 F. Deasphalted oil About 955 F. and above.

The heavy vacuum distillate and deasphalted oil are then separately extracted with the adulterated solvent from a post-hydrocracking extraction. Usually because the amount of solvent needed in the prehydrocracking extraction greatly exceeds that required in the post-extraction, a makeup amount of fresh or cleaned-up solvent is combined with the adulterated solvent from the post extraction containing the unstable materials removed from the hydrocracked product. This extraction is carried out as follows:

Solvent Temper- Raflinate dosage, ture, yield, percent F. percent Heavy vacuum distillate 150 220 ca. 69 Deasphalted oil 200 220 ca. 74

These fractions have approximately the following properties:

Unextracted fractions Extracted fractions Weight Weight percent API Conradson percent API, arogravity, carbon arogravity matics 60 F. number matics 60 F.

Heavy vacuum distillate 50. 4 21. 9 33 29 Deasphalted oil- 23 1. s-l. 9s 4s 26 The foregoing materials are blended to prepare feeds for hydrocracking as follows:

Percent Light vacuum distillate 29.1 Extracted heavy vacuum distillate 24.3 Extracted deasphalted oil 46.6

The properties of such blends are approximately as follows:

sulfied in about a 1:1 metals ratio on a silica alumina base. Catalyst temperature (avg.) 750. Space velocity (v./hr./v.) 1.0. Hydrogen pressure 2500.

Hydrogen consumption purity) s.c.f./bbl 1000.

Pressed oil from the dewaxer above is then charged to a rotating disc contactor about 3 inches in diameter which contains about 66 discs and is extracted at a temperature of approximately 120 F. using approximately 100 volume percent of furfural to produce a raffinate comprising approximately 97% of the charge to the extractor.

The raffinate is then distilled to produce three distillate fractions: N0. 1 (100 Neutral), No. 2 (200 Neutral), No. 4 (500 Neutral), and a bright stock. The properties of these products on a dewaxed basis are approximately as follows:

Total lube yield (based on vol. percent of charge to hydrocracker) 58.6 V.I. range 105-115 The color of the lube fractions separated into blending stocks consisting of a 100 Neutral, 200 Neutral, 500 Neutral, and a bright stock typically varies from about 0.25 to about 3.0 using ASTM color test D-1500.

DIAGRAMMATIC F LOW SCHEME An illustrative, diagrammatic representation of an overall flow scheme will be found beneficial and will now be set forth (with dewaxing omitted for simplicity). Such discussion is to be viewed in reference to the figure. The deasphalted residuum is charged via line 1 to a first hydrocracker feed or prehydrocracking extraction zone 2 wherein the residuum is extracted to remove a portion of the more aromatic materials according to the procedure described hereinabove. The rafiinate with a small amount of solvent entrained therein is charged via line 3 to a feed separation stage 4 wherein the solvent is removed, for example, by distillation. The lube oil raflinate recovered in 4 is charged to the hydrocracker 5 and is hydrocracked therein according to the procedure found hereinabove. The hydrocracked pro duct is charged through line 6 to the second extraction stage 7 and is solvent extracted with a fresh or purified solvent charge to achieve the degree of stability desired according to the procedure found hereinabove for such extractions. The raffinate from the second or product extraction stage 7 is charged via line 8 to a product separation stage (e.g., a distillation column) 9 wherein the finished lube oil product is separated from the entrained solvent and each is separately recovered. The solvent plus extract from the second extraction stage 7 is drawn oil through line 10 and is charged directly to the first extraction stage with a makeup amount of solvent, for example, via line 11. The solvent phase plus the aromatic extract is drawn oil from 2 through line 12 and is charged to a solvent recovery stage 13 where the solvent is purified, recovered, and is again used by charging to line 14 and/or line 15. The

extract and other impurities are drawn ofl? through line '16 and are recovered.

We claim: 1. A process for preparing high viscosity index lube 5 oils comprising:

(a) solvent extracting at least part of a lube oil fraction boiling above 650 F. with a solvent having preferential solubility for aromatics and which solvent comprises the adulterated solvent obtained from the extraction defined in (c) below to produce a rafiinate,

(b) hydrocracking the raffinate from (a) over a hydrocracking catalyst comprising a metal or the oxides or sulfides thereof which metal is selected from Groups VIB and VIII-B of the periodic system and combinations thereof, at from about 650 to 825 F. a pressure above 1,500 psi. and at a liquid hourly space velocity of from about 0.2 and 4.0, and

(c) solvent extracting the lube oil from (b) with a solvent having preferential solubility for aromatics.

2. The process of claim 1 wherein the solvent employed in the extractions is selected from the group consisting of furfural, phenol, acetophenone, acetonitn'le, nitrobenzene, aniline, 2,2-dichlorodiethyl ether, and dimethyl sulfoxide.

3. The process of claim 2 wherein the solvent is furfural, the extraction in (a) is carried out at from 125 to 325 F., and the extraction in (c) is carried out at from 80 to 130 F.

4. The process of claim 2 wherein the solvent is phenol, the extraction in (a) is carried out at from 150 to 255 F. and the extraction in (c) is carried out at from 106 to 140 F.

5. The process of claim 3 wherein the solvent to oil ratio in (a) is from about 4:1 to 0.8:1 and in (c) is from about 0.5:1 to 1.25:1.

6. The process of claim 4 wherein the solvent to oil ratio in (a) is from about 4:1 to 0.8:1 and in (c) is from about 0.5: 1 to 1.25:1.

References Cited UNITED STATES PATENTS 3,403,092 9/ 1968 Rausch 2081 8 3,414,506 12/1968 Campagne 20818 3,481,863 12/ 1969 Donaldson et a1 20818 3,488,283 1/1970 Button et al 208 l8 3,493,493 2/1970 Henke et a1. 208-48 50 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 

